Dye removal from denim scrap with a forced circulation kier

A process for liquid treatment of denim scrap to remove dye from the scrap and decolorize the scrap comprising the steps of:

• a) placing sufficient denim scrap pieces on a support surface to form a thickness
• of flat, layered denim scrap comprising individual denim pieces with opposed surfaces, the thickness having a top surface;
• b) applying a compression plate to said top surface to form the thickness of denim scrap into a compact cake;
• c) passing a first aqueous solution through the interior of the compact cake in a direction parallel to the surfaces of the scrap, the first aqueous solution passing between opposed surfaces of the denim pieces, the first aqueous solution containing reducing agent for indigo dye, whereby dye in the denim pieces is reduced to a soluble, reduced form, dissolves in the solution, and is removed from the denim scrap pieces;
• and
• d) passing a second aqueous solution through the interior of the compact cake in a direction parallel to the surfaces of the scrap, the second aqueous solution passing between opposed surfaces of the denim pieces, the second aqueous solution containing catalyzed hydrogen peroxide solution, the catalyst being an catalyzing amount of a transition metal cation or quaternaryalkylamine salt which catalyzes oxidation reactions of hydrogen peroxide, whereby indigo dye, other vat dyes, and sulfur dyes in the denim scrap pieces are bleached or destroyed to remove color therefrom.

A process for liquid treatment of denim scrap to remove dye from the scrap and decolorize the scrap comprising the steps of:

• a) placing sufficient denim scrap pieces on a support surface to form a thickness of flat, layered denim scrap comprising individual denim pieces with opposed surfaces, the thickness having a top surface;
• b) applying a compression plate to said top surface to form the thickness of denim scrap into a compact cake;
• c) passing a first aqueous solution through the interior of the compact cake in a direction parallel to the surfaces of the scrap, the first aqueous solution passing between opposed surfaces of the denim pieces, the first aqueous solution containing reducing agent for indigo dye, whereby dye in the denim pieces is reduced to a soluble, reduced form, dissolves in the solution, and is removed from the denim scrap pieces;
• and
• d) passing a second aqueous solution through the interior of the compact cake in a direction parallel to the surfaces of the scrap, the second aqueous solution passing between opposed surfaces of the denim pieces, the second aqueous solution containing an alkali metal hypochlorite whereby the indigo vat dye, other vat dyes, or sulfur dyes are bleached or destroyed.